An adapter for a target JDBC DataSource, applying the specified
user credentials to every standard getConnection() call, implicitly
invoking getConnection(username, password) on the target.
All other methods simply delegate to the corresponding methods of the
target DataSource.

Can be used to proxy a target JNDI DataSource that does not have user
credentials configured. Client code can work with this DataSource as usual,
using the standard getConnection() call.

In the following example, client code can simply transparently work with
the preconfigured "myDataSource", implicitly accessing "myTargetDataSource"
with the specified user credentials.

If the "username" is empty, this proxy will simply delegate to the
standard getConnection() method of the target DataSource.
This can be used to keep a UserCredentialsDataSourceAdapter bean definition
just for the option of implicitly passing in user credentials if
the particular target DataSource requires it.

doGetConnection

This implementation delegates to the getConnection(username, password)
method of the target DataSource, passing in the specified user credentials.
If the specified username is empty, it will simply delegate to the standard
getConnection() method of the target DataSource.